Capillary membranes of different compositions are known in particular because of their increasing use in dialysis or also in plasmapheresis. The use and the production of membranes, in particular of capillary membranes, in dialysis is described for example in the publication by Samtleben and Lysaght in: Hörl et al. Replacement of Renal Function by Dialysis 5th ed., Kluwer, 2004, pp. 709 to 724.
Thus WO 96/37282 describes a membrane, in particular for haemodialysis, which has a separating layer with a cut-off between 500 and 5000000 dalton, a supporting layer and a layer co-determining the hydraulic permeability, wherein the separation limit and hydraulic permeability are set mutually independently. However, it is very expensive to build up the membrane with different pore sizes within the individual layers.
EP 1547628 A1 describes plasma purification membranes and a plasma purification system, and in particular is geared towards specific physical properties, in particular the breaking resistance of the membrane due to the high stress load during plasma purification. This involves in particular protein and immunoglobulin permeability. In the membrane with a sponge-like structure, a gradient of the pore size is set, wherein a larger pore size is to be found on the outer surface than on the inner surface of the membrane.
U.S. Pat. No. 6,565,782 relates to synthetic polymeric microfiltration membrane materials with high surface porosity which can be obtained by co-casting a sulfone polymer with a hydrophilic polymer, such as polyvinylpyrrolidone. Disadvantages occur with this membrane in particular in relation to the separation of cellular components of the blood from the plasma phase, since the pressure on the blood cells caused by the use of small-pored membranes can lead to damage to the blood cells.
So-called hollow fibre spinnerets are used in most cases to produce such capillary membranes. An overview of this and other techniques for the production of hollow fibre membranes is disclosed in M. Mulder, Basic Principles of Membrane Technology second ed., Kluwer 1996, pp. 71-91.
When a hollow fibre membrane is produced by means of a hollow fibre spinneret, the hollow fibre membrane is produced in a so-called precipitation spinning process, wherein the polymers to be precipitated emerge from an annular slit of a spinneret arrangement, while the corresponding precipitant flows out of a central precipitant bore.
A hollow fibre spinneret of the named type is disclosed for example in DE 10211051 A1.